President Dmitry Medvedev says further study is needed for the project outside Moscow. Activists, who have enlisted the support of the singer Bono, are cautiously optimistic.

Reporting from Moscow — Russian President Dmitry Medvedev on Thursday announced that he had ordered highway work crews to stop cutting down trees in a renowned nature preserve outside Moscow. The statement came just hours after leaders of the ruling United Russia Party had urged him to reexamine the controversial project.

Despite previous government and judicial approval of the construction effort, the project "demands additional analysis," Medvedev said in the statement on his video blog.

The fate of the Khimki forest has become a flash point in recent months as civic groups have organized increasingly large protests against the project, a badly needed highway linking Moscow and St. Petersburg.

Activists reacted to Medvedev's statement with cautious optimism. "The war is not yet won, but it's a good claim to victory," said Yevgenia Chirikova, a young businesswoman and organizer of the Khimki opposition.

The forest, until recently a federally protected nature reserve, is part of the greenbelt outside the capital designed in Soviet times to manage Moscow's pollution. Plans for the project, unveiled in 2004, call for cutting a swath through centuries-old oak trees on the edge of a city long ago denuded of its greenery.

Opponents say the proposed route is not efficient, increasing travel time between the two cities, and that it opens the forest to further encroachment as development sprouts up next to the highway. They also allege that suggestions for bypassing the preserve, either a different route or a tunnel under the forest, fell on deaf ears and that most decisions were made in private.

The authorities had barreled through any dissent, insisting on pushing through the highway project as is. In November, Prime Minister Vladimir Putin signed an order changing the forest's zoning to one suited for transport and industry. In April, the Supreme Court ruled that the project was legal, and this summer the Federal State Enterprise Roads of Russia gave the highway the go-ahead.

The chopping — and the protests — started soon after.

In July, activists, drawing on tactics used in Western ecological protests, set up camp in the forest to monitor logging crews around the clock. The camps were quickly broken up by unidentified armed and masked guards, and the protesters driven from the site.

By the end of the month, the protests turned violent. Masked activists attacked the headquarters of the Khimki town administration, covering it in graffiti and bombarding it with smoke grenades. A week later, Chirikova was unceremoniously bundled off by Moscow police as she emerged from an independent news center in the capital, surrounded by stunned journalists. She was later released after paying a $50 fine.

But the forest's defenders got the Kremlin's attention Sunday with a rally in Moscow's historic Pushkin Square. It drew 3,000 people, a large number for a society not given to protests. Leading the demonstration was Russia's preeminent rocker, Yuri Shevchuk, who made headlines in May by criticizing Putin's policies to his face.

The final straw came Wednesday night when Irish rock star Bono, in U2's first performance in Russia, pulled Shevchuk onstage for a rendition of Bob Dylan's "Knockin' on Heaven's Door" in front of a crowd of 60,000. In an interview, Bono said he regretted not raising the issue of the Khimki forest during his Wednesday visit with Medvedev in the southern city of Sochi, having found out too late about an open letter to the singer signed by Shevchuk, Chirikova and thousands of others.

The president's quick action after the United Russia appeal spoke to an orchestrated attempt to head off growing protests before fall parliamentary elections and to not appear heedless of public discontent over the forest.

United Russia more logically might have appealed to Putin, the party's chairman, but the prime minister had personally pushed for the highway to be built. Recent reports have linked the highway construction contracts to Arkady Rotenberg, a businessman who is said to have been Putin's personal judo trainer.